Next, the researchers compared the bacterial composition of human stool samples with the tumor microbiome, finding that a quarter of the bacterial composition found in the stool (which is a measure for the gut microbiome) was consistent with the tumor microbiome.
Senior author Florencia McAllister, MD, assistant professor of clinical cancer prevention at MD Anderson, Houston, Texas, told Cancer Therapy Advisor that this finding could suggest that the bacteria from the gut may translocate into the tumor. Conversely, this could also lead to the suggestion that tumor bacteria can be modulated by adjusting the gut bacteria.
As a result of these findings, mice were implanted with tumor cells from mice cancer cell lines and then transplanted with human fecal samples from long-term survivors who had no evidence of disease, patients with pancreatic cancer who were predicted to be short-term survivors, or healthy patients. Mice that received fecal transplants from long-term survivors had significantly smaller tumors compared with mice that received fecal transplants from short-term survivors (P <.001) or healthy patients (P =.02).
Although Dr Miller described the study as “impressive” and “important,” he expressed concern about the microbial signature. He said when it comes to bacteria, one doesn’t know if the findings are universally applicable or just limited to that study population because there’s such baseline bacterial diversity among different geographic areas. “If you’re going to say that these 4 bacteria are a biomarker of long survival, I don’t know if it’s the same in Timbuktu,” he said.
As for what comes next, Dr McAllister said she wants to understand how the bacteria get into the tumor and whether those bacteria themselves are actually important, or just serve as a biomarker for outcome. In addition, she said, these findings need to be evaluated in a small study of patients to show whether the tumor microbiome in patients can be changed by changing the gut microbiome and whether immune suppression can be reversed.
Disclosure: Dr McAllister and 2 of her coauthors are filing a patent based on these research findings.
Riquelme E, Zhang Y, Zhang L, et al. Tumor microbiome diversity and composition influence pancreatic cancer outcomes. Cell. 2019;178(4):795-806.